A fighter in an Afghan local defence militia opened fire on his American
allies and killed two in the latest example of the growing insider threat to
Nato forces.

The killing came just hours after a message purporting to be from Mullah Mohammad Omar, fugitive leader of the Taliban, boasted the insurgents had widely infiltrated the Afghan forces to launch such attacks.

It was the sixth similar incident in the country in the past fortnight. Nato and Afghan commanders have tightened security and vetting to try and contain the threat.

A newly recruited member of the Afghan Local Police, a village defence force trained by international forces, opened fire in Farah province when he was given a weapon for a training session. American and Afghan forces shot back and killed him.

Hours later an Afghan army soldier fired on American troops in Kandahar, wounding two.

At least 37 foreign troops have been killed in such attacks this year alone. Seven were British.

The Taliban’s statement to mark the Islamic holiday of Eid ul-Fitr said the militants had “cleverly infiltrated in the ranks of the enemy according to the plan given to them last year”.

“Many conscious Afghans in the rank and files of the enemy have shown willingness to help the Mujahideen”, it claimed.

“As a result, the foreign invaders and their allies in their military centres and bases do come under crushing blows of these heroic soldiers.”

Both Afghan and Nato commanders have sought to play down the extent of infiltration. Most of the attacks were rooted in combat stress, personal disputes, or cultural misunderstandings which had flared into violence, they say.

Earlier this week the senior British officer in the country told The Daily Telegraph that “a small amount can be directly attributed to insurgent infiltration or influence”.

Lt Gen Adrian Bradshaw said: “Of course we are very alive to that threat. When you look at it from the insurgent’s point of view why wouldn’t they try and attack us any way they can?”

Up to 300 extra specialist counter intelligence personnel have been drafted into the Afghan army to spot potential assassins.

The head of the Afghan army has ordered that 150,000 soldiers, – three quarters of the force — to be reinvestigated for security vetting and to be enrolled on a biometrics database.

Hundreds of soldiers who have shown signs of radicalisation, including travel to and from Pakistan, have been discharged.

The lengthy Taliban statement boasted of military successes but also appeared to suggest that they would consider a power sharing government with other Afghan factions.

Many Afghans, including remnants of the powerful Northern Alliance bloc which fought the Taliban in the 1990s, are fiercely opposed to any concessions to the insurgents.